Query: SCSI Device node creation when UFS is loaded as a module

Query: SCSI Device node creation when UFS is loaded as a module

[asutoshd]

Hi
I'm loading the ufs-qcom driver as a module but am not seeing the 
/dev/sda* device nodes.
Looks like it's not being created.

I find the sda nodes in other paths being enumerated though:

/ # find /sys -name sda
/sys/kernel/debug/block/sda
/sys/class/block/sda
/sys/devices/platform/<...>/<xxx>.ufshc/host0/target0:0:0/0:0:0:0/block/sda
/sys/block/sda

All Luns are detected and I see sda is detected and prints for all the 
Luns as below -:
sd 0:0:0:0: [sda] .... ....-byte logical blocks:

... so on ...

But if I link it statically instead of a module, it works fine. All 
device nodes are created.

I'm trying to figure out where/how in SCSI does it create these device 
nodes - /dev/sd<a/b/c/d> ?
I've looked into sd.c but I couldn't figure out the exact place yet.

Any pointers please?

TIA

-asd

RE: Query: SCSI Device node creation when UFS is loaded as a module

[Avri Altman]

> 
> Hi
> I'm loading the ufs-qcom driver as a module but am not seeing the
> /dev/sda* device nodes.
> Looks like it's not being created.
> 
> I find the sda nodes in other paths being enumerated though:
> 
> / # find /sys -name sda
> /sys/kernel/debug/block/sda
> /sys/class/block/sda
> /sys/devices/platform/<...>/<xxx>.ufshc/host0/target0:0:0/0:0:0:0/block/sda
> /sys/block/sda
> 
> All Luns are detected and I see sda is detected and prints for all the Luns as
> below -:
> sd 0:0:0:0: [sda] .... ....-byte logical blocks:
> 
> ... so on ...
> 
> But if I link it statically instead of a module, it works fine. All device nodes are
> created.
> 
> I'm trying to figure out where/how in SCSI does it create these device nodes -
> /dev/sd<a/b/c/d> ?
> I've looked into sd.c but I couldn't figure out the exact place yet.
> 
> Any pointers please?
I guess it's most probably in scsi_sysfs_add_devices, part of the async scan:
ufshcd_async_scan-> ufshcd_probe_hba-> scsi_scan_host->__scsi_scan_target-> scsi_probe_and_add_lun...

Thanks,
Avri

Re: Query: SCSI Device node creation when UFS is loaded as a module

[Steffen Maier]

On 10/24/19 1:51 AM, asutoshd@codeaurora.org wrote:
> Hi
> I'm loading the ufs-qcom driver as a module but am not seeing the /dev/sda* 
> device nodes.
> Looks like it's not being created.
> 
> I find the sda nodes in other paths being enumerated though:
> 
> / # find /sys -name sda
> /sys/kernel/debug/block/sda
> /sys/class/block/sda
> /sys/devices/platform/<...>/<xxx>.ufshc/host0/target0:0:0/0:0:0:0/block/sda
> /sys/block/sda
> 
> All Luns are detected and I see sda is detected and prints for all the Luns as 
> below -:
> sd 0:0:0:0: [sda] .... ....-byte logical blocks:
> 
> ... so on ...
> 
> But if I link it statically instead of a module, it works fine. All device 
> nodes are created.
> 
> I'm trying to figure out where/how in SCSI does it create these device nodes - 
> /dev/sd<a/b/c/d> ?

That's from (systemd-)udevd user space based on uevents from the kernel.

> I've looked into sd.c but I couldn't figure out the exact place yet.

Yeah, based on the SCSI device probe and add lun, the high level driver sd 
would emit udev events for block devices.


-- 
Mit freundlichen Gruessen / Kind regards
Steffen Maier

Linux on IBM Z Development

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Re: Query: SCSI Device node creation when UFS is loaded as a module

[asutoshd]

On 2019-10-24 02:50, Steffen Maier wrote:
> On 10/24/19 1:51 AM, asutoshd@codeaurora.org wrote:
>> Hi
>> I'm loading the ufs-qcom driver as a module but am not seeing the 
>> /dev/sda* device nodes.
>> Looks like it's not being created.
>> 
>> I find the sda nodes in other paths being enumerated though:
>> 
>> / # find /sys -name sda
>> /sys/kernel/debug/block/sda
>> /sys/class/block/sda
>> /sys/devices/platform/<...>/<xxx>.ufshc/host0/target0:0:0/0:0:0:0/block/sda
>> /sys/block/sda
>> 
>> All Luns are detected and I see sda is detected and prints for all the 
>> Luns as below -:
>> sd 0:0:0:0: [sda] .... ....-byte logical blocks:
>> 
>> ... so on ...
>> 
>> But if I link it statically instead of a module, it works fine. All 
>> device nodes are created.
>> 
>> I'm trying to figure out where/how in SCSI does it create these device 
>> nodes - /dev/sd<a/b/c/d> ?
> 
> That's from (systemd-)udevd user space based on uevents from the 
> kernel.
> 
>> I've looked into sd.c but I couldn't figure out the exact place yet.
> 
> Yeah, based on the SCSI device probe and add lun, the high level
> driver sd would emit udev events for block devices.

Thanks Steffen and Avri.

I understood that sd.c creates the devices based on scsi_device and 
establishes a relation between scsi_device (sdp) and scsi_disk (sdkp).
But I couldn't figure out why it creates the device fine when the 
ufs-qcom is linked statically, but is unable to create the devices when 
inserted as a module.

Does it follow a different method to create the device nodes when 
statically linked and needs (systemd-)udevd to handle the events during 
dynamic insertion?

Thanks
asd